Set up on US-occupied Cuban territory, it was filled with supposed "enemy combatants" seized in post-invasion Afghanistan, the vast majority of whom were then held without charge or trial, brutalised and tortured. That was all supposed to have come to an end after Obama's election.

But instead of shutting this monstrosity, the camp is being rebuilt. Congress has played a central role in keeping Guantánamo open. But the president only tried to move it to Illinois, not end the scandal of indefinite detention without trial. And he's personally blocked the release of dozens of prisoners, even when they've been cleared.

That's at the heart of why the detainees are striking. Among them is Shaker Aamer, a Saudi-born British resident held without charge for 11 years, much of it in solitary confinement. As with half of the rest of the prisoners, the US authorities now accept that there is no case against him, and he was cleared for release six years ago.

Aamer hasn't seen his family since 2001, and has never met his 11-year-old son, Faris. He has refused food for 71 days, and his case is due to be debated tomorrow in parliament in response to a petition of over 100,000 names. But it now turns out that, uniquely among the prisoners, Aamer has been cleared for release to only one country: Saudi Arabia.

Despite the British government's claims to be lobbying for his return to London, the evidence suggests neither London nor Washington wants anything of the kind. As Aamer's lawyer, Clive Stafford Smith, puts it: "The sole reason to send Shaker to Saudi Arabia is to have him silenced, most likely by sentencing him to a long imprisonment after a sham trial."

The reason is not hard to find. Soon after he was seized, Aamer says he was assaulted and tortured (into falsely confessing links to al-Qaida) by US officials at Bagram air base in Afghanistan in the presence of MI6 officers – abuse that continued at Guantánamo. Even more dangerously, he was also present, along with British intelligence agents, when Ibn al-Sheikh al-Libi was tortured at Bagram into alleging that Saddam Hussein was training al-Qaida terrorists – bogus claims Bush and Colin Powell used to justify the invasion of Iraq.

The Metropolitan police has now opened three new investigations into UK intelligence collusion with torture and "rendition", including Aamer's case. That's on top of MI6's role in the kidnapping of Libyan dissidents and their families in 2004, for which the government has already paid out over £2m in compensation.

Earlier this month Scotland Yard detectives interviewed Aamer in Guantánamo. No wonder the British government is so keen to force through secret court hearings in "national security" cases through its justice and security bill – or that it has struggled to convince the courts that the Salafist cleric Abu Qatada, regularly detained without charge for years, would not be at risk of torture if packed off to a police state such as Jordan.

It's hardly surprising in the wake of such a saga that western claims to be the champions of human rights and humanitarian intervention are treated with derision across much of the world. But as its dirty secrets are seeping out, the war on terror itself has already mutated.

Obama hasn't closed Guantánamo or held those who authorised these barbarities to account. But US torture camps and boots on the ground are on the way out. Their place has been taken by air and proxy campaigns, such as in Libya and Syria, and drone wars that have already killed thousands in Pakistan, Yemen and Somalia – but are more popular at home.

We don't yet know the motivations of the two men accused of carrying out last week's atrocity in Boston, which killed three people and seriously injured many more. But we do know that 61 were killed the same day in bomb attacks in Iraq that were blamed on al-Qaida, brought to the country by the US-British invasion. And 16 were killed in Pakistan the following day in a suicide attack claimed by the Pakistani Taliban, which mushroomed as a result of the invasion of Afghanistan.

What is certain is that so long as the US and its allies intervene, occupy and wage war across the Arab and Muslim world – whether directly or by proxy, with daisy cutters or drones – such outrages will continue. It's the logic of a war of terror without end.